1986 Corvette R-12 to R-134a Conversion

[JohnHere]

I will weigh in the remaining 11 oz. Do I add as a liquid on the low side?

Negative. With the engine and compressor running, charge gas-only into the low side, keeping the low-side handwheel open and the high-side handwheel closed on your Manifold Gauge Set until you reach the full calculated charge weight. Then close the low-side MGS handwheel as well.

[kenlou]

OK, but remember, the compressor is not running at this time. How wouldI add more with the engine off?
I have someone that will evacuate the refrigerant after for me to determine exactly how much is in there. I want to add that last 11 oz.

[JohnHere]

If the static pressure of the system is roughly equal to the refrigerant container's pressure, no refrigerant will flow into the system, either liquid or gas, if the compressor isn't running. Hopefully, the static pressure is a little lower than the container's pressure, so as you begin to charge, that little bit will allow the compressor to engage. If not, you could try warming the container using a blanket heater designed for 30-pound cylinders, or warm water immersion if using a small can.

[kenlou]

So then I am going to have to jumper the low pressure switch?

[JohnHere]

I don't recommend forcing the compressor to run because there might not be enough refrigerant in the system to return oil to the compressor, starving it for lubrication, and causing an internal compressor failure. If it doesn't engage as you begin the charging procedure, then the can-warming trick should do it.

I don't recall anymore, but did you measure the static pressure with the partial charge in it? If the SP is above ~50 PSI, the refrigerant probably won't flow into the system without warming the container to increase its pressure.

[tbirdtbird]

I am trying to remember why we only partially charged this system from the get go. Verrry long thread, you lose track...

[JohnHere]

I know, tbirdtbird. I believe it was because of not wanting to keep the system under vacuum during the winter.

[kenlou]

Okay, as to where we are with this……
This car had been sitting for 25 years and I decided to get the AC working. From the get go, I decided to convert to 134a.
My initial plan was to get all the new parts installed and take it to an AC shop and have it finished there. I was told by several people that I could do it myself, and considering the $$$ involved, I decided to do what I could.
With the help of you guys here, I was able to get the system evacuated and checked for and fix the leaks. Convinced I had a good vacuum after a couple of days, and considering it was December in Illinois at this time, I followed your advice and put in a partial charge until spring.
I used a scale and kept track of the the precise weight I put in it so that I could follow-up weighing in the rest of the refrigerant in the Spring.
I used pure 134 without any additives and let the vacuum suck 25.6 oz of refrigerent into the system and put the caps (they do have rubber gaskets) on both adapters.

So here it is Spring and I am anxious to get this finished.

I have decided to follow your advice and take it to an AC shop and let them recover/evacuate/recharge. It definitely seems like the best way to know how much of that initial holding charge is still in there.

I will keep you informed.

[tbirdtbird]

I like this plan....

[JohnHere]

I have decided to follow your advice and take it to an AC shop and let them recover/evacuate/recharge. It definitely seems like the best way to know how much of that initial holding charge is still in there.

Right you are. It's the only way to judge whether any refrigerant leaked out during the winter.